It was 1970. They worked 15-hour days. They stuffed a lot of envelopes.

And, at first, they didn't like the name.

"Who in the hell do they think we are, the Grange?" Stephen Cotton recalled about reading the name an advertising agency had proposed for their national protest. Earth Day sounded like an event for farmers. "But it grew on us."

Earth Day turns 40 on Thursday, making its founders 60-somethings. To this group of about 20, both the day and the country look very different now.

In those four decades, the angrier, more ambitious environmental movement that sprang out of Earth Day made vast changes in Washington. New federal laws took on dirty air and poisoned water -- and won.

But today, American environmentalism is struggling in a new kind of fight.

The problems are more slippery: pollutants like greenhouse-gas emissions, which don't stink or sting the eyes. And current activists, by their own admission, rarely muster the kind of collar-grabbing immediacy that the first Earth Day gave to environmental causes.

"I don't think we've come up with a good way in the conservation movement of making it real for people," said Arturo Sandoval, who was 22 when he organized activities across the West on the first Earth Day.

In 1970, "you could say, 'Have you been down to the river lately?' And people would say, 'Oh my God, I don't even let my kids go there,' "said Sandoval, now 62 and still working on environmental causes in Albuquerque. "Global warming, to most people, is an abstract issue."

A 'human jam'

Earth Day's 40th anniversary will be celebrated across the globe Thursday: There will be children studying pollution in Baltimore Harbor, volunteers cutting down invasive ivy in the District, a coral-reef cleanup in the Virgin Islands, a concert in Rome.

On Sunday, a climate-focused rally on the Mall will include performances by Sting, John Legend and the Roots.